Process of preparing explosive charges



Patented Dec. 8, 1936 UNITED STATES PATENT OFFICE PROCESS OF PREPARING EXPLOSIVE CHARGES No Drawing. Application August 8, 1934, Serial No. 738,936

- 22 Claims.

This invention relates to an improved process for preparing explosive charges, and more particularly to a process for filling containers with explosive charges that are of relatively high 5 density but not suitable for production in cast form.

While ammonium nitrate is a very suitable explosive ingredient, it alone is not adapted for use as a practical blasting agent. While it is in fact an explosive material, it is incapable of detonation by the usual priming agents, and does not possess suflicient sensitiveness alone to propagatethe detonation wave under the conditions of use, either in military or commercial operations. For this reason it is necessary to incorporate sensitizing agents with ammonium nitrate. In the case of the commercial dynamites,

nitroglycerin is the usual sensitizer. In like manner, military explosives of the Amatol type have consisted of combinations of ammonium nitrate and trinitrotoluene, the proportions used varying between 40 to 80% ammonium nitrate and 60 to trinitrotoluene.

Ammonium nitrate disruptive explosives, as described in the foregoing, have been used very satisfactorily in general. Certain difliculties are encountered in their use at times, however. When Amatol of the composition of 40 parts ammonium nitrate and 60 parts trinitrotoluene is loaded into shells, the trinitrotoluene content is sumciently high so that the mixture can be poured and cast. In this case, the poured material consists of solid ammonium nitrate suspended in molten trinitrotoluene. When an 80-20 mixture of the same ingredients is used, however, it is necessary to press or extrude the hot mixture into the shell. Here again the ammonium nitrate is in solid and the trinitrotoluene in liquid condition; the molten material lubricates the solid material and helps to compact the charge within the shell by filling the interstices between the ammonium nitrate particles. Under some conditions, this composition is not sufliciently plastic and smooth-flowing to load readily. 45 An object of our invention is an improved process for preparing explosive charges of relatively high density, but not in cast form. A

further object is such a process in which ammonium nitrateexplosives are prepared of a additional object is to render the ammonium nitrate plastic so that a wide range of sensitizing agents may be used. Further objects will be disclosed and will become apparent as the invention is described hereinafter.

We have found that satisfactory high density ammonium nitrate explosives, from the point of view of loading properties, may be produced it the ammonium nitrate is heated, in the presence of a freezing point depressant therefor, to a 10 temperature sufficient to liquefy a portion of the ammonium nitrate but at which some of the explosive composition is in the solid state. The explosive is then compacted while still hot by any of several known methods, such as ex- 15 truding, pressing, tamping, and the like, preferably in a container, and the charge is cooled to obtain it as a. high density explosive in a firm solid mass, but not in cast form.

Various types of compounds are adapted for 20 eflicient use as freezing point depressants. Two general divisions of such compounds may be given as (1) materials which are liquid at the temperature used and in which ammonium nitrate is at least slightly soluble, and (2) salts 25 which depress the freezing point of ammonium nitrate when mixed therewith. As materials of the first class, we may, for example, employ a solid, aliphatic basic compound such as urea, dicyandiamid, guanadin, or acetamide. Prefer- 0 ably, we use urea as a representative of this group. Another compound of the first class which is useful for plasticizing ammonium nitrate is water, and we find this a very effective medium for the purpose. The second class of 35 compounds satisfactory for improving the flowing properties of ammonium nitrate according to our invention comprises salts other than ammonium nitrate, preferably other nitrates or other ammonium salts, although a wider range 40 of salts than these may be used. As examples of this class we may cite sodium, potassium, magnesium, and calcium nitrates.

Ammonium nitrate by itself is in general not suflicientlysensitive for use as an explosive, es- 45 pecially in the small diameters or comparatively small size of charge customarily employed in blasting or in shell loading. For this reason, we prefer to include a sensitizing agent with the plasticized ammonium nitrate in order to attain 5n the desired sensitiveness and propagating power. As such agent, we find the solid organic explosive compounds the most desirable, for example trinitrotoluene, picric acid, ammonium picrate, nitrostarch, pentaerythritol tetranitrate, cyclotri- 55 methylene-trinitramine, tetryl and the like. Liquid sensitizers, such as, for'example, nitroglycerin, may also be used. In the case of nitroglycerin, it is necessary to have sufficient freezing point depressant to lower the plasticizing temperature to a point at which nitroglycerin is safe to handle in the presence of ammonium nitrate. Other liquid sensitizers, such as nitrobenzene, dinitrotoluene and hydrocarbons may also be used. Where the plasticizing temperatureis sufficiently low, organic combustibles may satisfactorily be used. Other sensitizing materials may be used to advantage, however, such as for examplemetallic sensitizers, preferably in finely divided condition, and as such materials we may employ metallic aluminum, ferrosilicon, calcium silicide, and other like agents. A

As an illustration of one method of carrying out ourinvention we will describe the procedure followed in preparing a high density charge from a composition comprising 80% ammonium nitrate, 16% trinitrotoluene, and 4% urea. The mixture is heated to atemperature of 90 C. in a steam-jacketed kettle. The presence of the urea is sufiicient at this temperature to liquefy an amount of ammonium nitrate equivalent to about 12% ofthe entire composition. Since the temperature is above the fusion point of trinitrotoluene, this latter material is also in molten condition,.making a total liquid content of 32%. The foregoing composition is loaded into a shell or other container and tamped to a relatively high density. The compacted material is then allowed to cool and form a firm solid mass. In the example cited, 4% of urea was used to replace the same amount of trinitrotoluene of an 80-20 ammonium nitrate-trinitrotoluene composition. The presence of the urea greatly improves the loading properties of the mixture because of its liquefying ability toward ammonium nitrate.

Urea may be used also to replace some of the ammonium nitrate, but greater economic advantage is obtained by replacement of the trinitrotoluene. As the presence of the urea brings about, in general, a slight desensitizing effect, probably because of the higher densities obtained, a sufficient amount of sensitizing agent should be used. Preferably our compositions containing urea will include ammonium nitrate as the predominant ingredient, 1 to 10% urea and 5 to 25% trinitrotoluene.

Similarly high density ammonium nitrate charges, according to our invention, may be prepared by use of water as a freezing point depressant. When ammonium nitrate is heated to 90 C. with 3 parts of water, the water dissolves approximately 27 parts of ammonium nitrate, so that a liquid content of about 30% of the entire composition is present. While. such a mixture is we employ a sensitizing agent having a melting point above the temperature of heating, for example pentaerythritol tetranitrate. In such compositions, when ammonium nitrate is present as the predominant ingredient, we preferably use Trinitrotoluene can be used as a sensibetween 2 and 25% pentaerythritol tetranitrate and 1 to 8% water.

While we have described the use of water in the foregoing for the purpose of liquefying a portion of the ammonium nitrate present, we may use such proportions of ingredients that the water will dissolve and liquefy all the ammonium nitrate, in which case the resulting ammonium nitrate solution will serve in the production of a high density explosive in conjunction with an explosive ingredient not liquefied. As such explosive ingredient, pentaerythritol tetranitrate will serve satisfactorily, since it possesses a relatively high fusion point.

The procedure in preparing high density ammonium nitrate explosives with the use of water as freezing point depressant is similar to that given in the foregoing in the case of urea, except that, with water present, it may be desirable to dry the compacted explosive charge to remove the excess water, especially when the presence of the water renders the explosive too insensitive.

Whilewe have given specific illustrations of the use singly of two of the different types of freezing point depressants cited, it should be understood that more than one of the depressants may be used in the same explosive charge. In the case of the composition containing pentaerythritol tetranitrate and employing water as freezing point lowering agent, the presence of urea also would give an additive depressant effect and at the same time would have a stabilizing influence on the nitric ester.

It will be understood that our process for forming relatively high density ammonium nitrate explosive charges contemplates the loading of the material into containers while in semi-solid condition. Cast explosives have been employed in the prior art but such a form of the material is outside the scope of our invention. Cast charges possess the disadvantage of contracting on cooling, thereby leaving cracks throughout the charge and not filling the container completely with a firmly packed mass. The high density compact explosive according to our invention is free of these disadvantages, since only a portion of the charge is liquefied and the liquefied portion aids in compacting the permanently solid portion. According to our method also, it is possible to work at lower temperatures than would otherwise be the case, thereby increasing the safety of the operation.

The temperature used to plasticize the ammonium nitrate may be relatively high, for example, above 100 C. if the sensitizer is sufiiciently stable to withstand this temperature, and it should be desirable to use a minimum of plasticizing agent. On the other hand, by the use of larger amounts of freezing point depressants, the ammonium nitrate may be plasticized at a relatively low temperature for example, around 40 C. or lower. This low temperature makes it safe to use certain combustible materials and a wide range of sensitizing agents which could not otherwise be used safely at the higher temperatures necessary.

Our invention is applicable to various types of ammonium nitrate explosives, where a high density compact mass is desirable. It may be used, for example, in safety explosives, in explosives for the loading of shells and other containers to be disrupted, in relatively insensitive explosives of the Favier type, and in other compositions.

While we have described our invention in considerable detail in the foregoing, it will be understood that many variations may be made in the procedure and compositions without departing from the spirit of the invention. We intend therefore to be limited only as indicated in the I following patent claims.

We claim:

1. In the process of preparing relatively high density explosive charges, the steps which comprise incorporating ammonium nitrate and a freezing point depressant, to produce a compo.- sition which has a relatively broad melting point range and heating to a temperature sufiicierit to liqueiy a portion only of the ammonium nitrate with the freezing point depressant.

2. The process of preparing relatively high density explosive charges containing ammonium nitrate as the principal ingredient, which comprises incorporating with sail ammonium nitrate a sensitizing ingredient and a freezing point depressant, to produce a composition which has a relatively broad melting point range, heating the composition to a temperature suflicient to liquefy a portion of the ammonium nitrate, compacting the explosive charge while hot, and cooling the charge to form it into a firm, solid mass.

3. The process of preparing relatively high density explosive charges containing ammonium nitrate which comprises incorporating with said ammonium nitrate a sensitizing ingredient and a freezing point depressant, to produce a composition which has a relatively broad melting point range, heating the composition to a temperature sumcient to liquefy at least a portion of the ammonium nitrate while maintaining a part of the composition in the solid state, compacting the explosive charge while hot, and cooling to solid ify the product.

4. The process of claim 2, in which the sensitizing ingredient is a solid organic explosive compound.

5. The process of claim 2, in which the sensitizing ingredient is taken from a group consisting of trinitrotoluene, picric acid, ammonium picrate, nitrostarch, pentaerythritol tetranitrate, cyclotrimethylene trinitramine, and tetryl.

6. The process of claim 2, in which the sensitizing ingredient is a non-explosive, combustible material.

7. The process of claim 2, in which the sensitizing ingredient is taken from a group consisting of aluminum, ferrosilicon and calcium silicide.

8. The process of claim 2, in which the freezing point depressant is an aliphatic basic compound.

9. The process of claim 2, in which the freezing point depressant is urea.

10. The process of claim 2, in which the freezing point depressant is a salt fusible with ammonium nitrate.

11. The process of claim 2, in which the freezing point depressant is a compound taken from agroup consisting of sodium nitrate, potassium nitrate, calcium nitrate, and magnesium nitrate.

12. The process of claim 2, in which the freezing point depressant is water.

ing point depressant is a substance which is liquid at the temperature of heating and in which ammonium nitrate is highly soluble.

14. The process of filling containers with relatively high density explosive charges containing ammonium nitrate as the principal ingredient which comprises heating said ammonium nitrate with 5 to 25% trinitrotoluene and 1 to urea to a. temperature sufficient to liquefy only a portion of the ammonium nitrate, filling the explosive charge into the container and compacting it therein, and cooling the charge to form it into a firm, solid mass. 1

15. The process of filling containers with relatively high density explosive charges containing ammonium nitrate as the principal ingredient which comprises heating said ammonium nitrate with 2 to 25% of pentaerythritol tetranitrate and 1 to 8% of water to a temperature sufiicient to liquefy only a portion of the explosive charge, filling said charge into the container and compacting it therein, and cooling the charge form it into a firm, solid mass.

16. The process of claim 15, in which the sensitizer is trimethylene trinitramine.

17. The process of compacting explosives containing ammonium nitrate, which comprises heating the ammonium nitrate in the presence of a freezing point depressant producing a composition which has a relatively broad melting point range, fusing a portion only of the ammonium nitrate and cooling the product to form a solid mass.

18. The process of preparing relatively high density explosive charges containing ammonium nitrate as the principal ingredient, which comprises incorporating with said ammonium nitrate a sensitizing ingredient and afreezing point depressant comprising water, heating the composition to a temperature sufficient to liquefy a portion of the ammonium nitrate, compacting the explosive charge while hot, cooling the charge to form it into a firm, solid mass, and drying the product.

19. The process of compacting a solid organic explosive compound to a high density charge which comprises incorporating said compound with ammonium nitrate and a freezing point depressant, to produce a composition which has a. relatively broad melting point range, heating the composition to a temperature below the fusion point of the organic explosive compound but at which the ammonium nitrate is liquefied, and cooling the charge to form it into a firm, solid mass.

20. The process according to claim 19, in which the freezing point depressant is water.

21. The process according to claim 19, in which the freezing point depressant is urea.

22. The process according to claim 19, in which the freezing point depressant is a. substance in which ammonium nitrate is highly soluble and is liquid at the temperature of heating.

CLIFFORD A. WOODBURY. PHILIP G. WRIGHTSMAN. 

